Nonmuscle myosin II molecules carry out a wide variety of functions within cells. There are three nonmuscle myosin II genes. We have studied the strain dependence of the ADP release mechanism in nonmuscle myosin IIA and IIB using a solution kinetic approach. The results show that positive strains accelerate the rate of ADP release whereas negative strain markedly lowers the rate. These results suggest that these myosins, and particularly nonmuscle myosin IIB, are ideally suited to act as tension bearers in cells. We are now using optical trapping nanometry to extend these studies on both nonmuscle myosin IIA and IIB. Preliminary results with nonmuscle myosin IIB indicate that it has long attachment times as would be expected from such a slow myosin. We have expressed nonmuscle myosin IIA with a GFP-tagged regulatory light chain (RLC) with particular interest in whether the myosin would still adopt the off state when this light chain is not phosphorylated. The data show that the GFP tag does not interfere with regulation of the myosin.